Re: v4l library - decoding of Pixart JPEG frames - Jean-Francois Moine

From: Jean-Francois Moine <moinejf@free.fr>
To: Hans de Goede <j.w.r.degoede@hhs.nl>
Cc: Magic Banana <magicbanana@gmail.com>,
	Video 4 Linux <video4linux-list@redhat.com>
Subject: Re: v4l library - decoding of Pixart JPEG frames
Date: Mon, 18 Aug 2008 09:34:24 +0200	[thread overview]
Message-ID: <1219044864.1707.21.camel@localhost> (raw)
In-Reply-To: <48A80FC7.6090909@hhs.nl>

On Sun, 2008-08-17 at 13:47 +0200, Hans de Goede wrote:
> Hi Jean, Thomas,

Hi Hans,

> Jean, good to see that you are working on the pixart 73xx support, I 
> have a cam over here as well which didn't work at all, now with your 
> fixes, it atleast generates proper frames (they used too be much too 
> small). Unfortunately my cam still does not work, your siv.c does show 
> something which seems to be decoded video data, but not as it should 
> look like, from the looks of it we are close though.
> 
> I've made a single raw frame from my cam available here:
> http://people.atrpms.net/~hdegoede/image.dat

I forgot to give you the command:

	siv -p PJPG -f 480x640 -d image.dat

('-p PJPG' gives the encoding and '-f 480x640' because the image is
turned to the left).

It is almost black and white with high contrast.

> If anyone can write code which can convert that to an image (might be 
> unsharp) that would be great!
> 
> I've done a first attempt at making v4lconvert handle these pixart jpeg 
> frames, patch attached. Warning this is a crude hack breaking regular 
> jpeg support. This seems to work less well with my cam then the siv.c 
> code, so we might need to make more changes either to v4lconvert, or 
> maybe to the jpeg_put_header call in pac7311.c, talking about this call, 
> since we are defining a custom format anyways, shouldn't we just omit 
> the header and send the jpeg-ish pixart frame data to userspace as is?

About the header, it seems that neither the previous (in pac7311.c), nor
the standard jpeg header (in jpeg.h) give good results.

> Thomas, I would be very much interested in your tinyjpeg version with 
> pixart support!
> 
> Jean, perhaps you can make some raw images from your cam available 
> somewhere too?

I am working with a french guy (Magic Banana, in Cc) who has a webcam
with a 7302 sensor. I put an image extracted from a MS-win trace in my
site:

	http://moinejf.free.fr/pac7302.dat

(I added a jpeg header).

Cheers

-- 
Ken ar c'hentañ |             ** Breizh ha Linux atav! **
Jef             |               http://moinejf.free.fr/

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